Poly-component blade for a steam turbine

ABSTRACT

A steam turbine blade, such as those used in an electric power generation steam turbine, has an airfoil portion. The airfoil portion includes a metallic section consisting essentially of metal and at least one (lightweight) panel section not consisting essentially of metal. The metallic section extends from generally the blade root to generally the blade tip. Each panel section is an elastomeric section. The metallic section and the at-least-one panel section only together define a generally airfoil shape.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent application is a continuation-inpart application ofU.S. patent application Ser. No. 08/650,278 by John J. Fitzgerald et al.which is entitled "Poly-Component Blade for a Gas Turbine" and which wasfiled May 20, 1996, now abandoned.

FIELD OF THE INVENTION

The present invention relates generally to gas and steam turbines, andmore particularly to a steam turbine blade composed of two or morecomponents made from different materials.

BACKGROUND OF THE INVENTION

Gas turbines include, but are not limited to, gas turbine powergeneration equipment and gas turbine aircraft engines. A gas turbineincludes a core engine having a high pressure compressor to compress theair flow entering the core engine, a combustor in which a mixture offuel and the compressed air is burned to generate a propulsive gas flow,and a high pressure turbine which is rotated by the propulsive gas flowand which is connected by a larger diameter shaft to drive the highpressure compressor. A typical front fan gas turbine aircraft engineadds a low pressure turbine (located aft of the high pressure turbine)which is connected by a smaller diameter coaxial shaft to drive thefront fan (located forward of the high pressure compressor) and to drivean optional low pressure compressor (located between the front fan andthe high pressure compressor). The low pressure compressor sometimes iscalled a booster compressor or simply a booster.

The fan and the high and low pressure compressors and turbines have gasturbine blades each including an airfoil portion attached to a shankportion. Rotor blades are those gas turbine blades which are attached toa rotating gas turbine rotor disc. Stator vanes are those gas turbineblades which are attached to a non-rotating gas turbine stator casing.Typically, there are alternating circumferential rows ofradially-outwardly extending rotor blades and radially-inwardlyextending stator vanes. When present, a first and/or last row of statorvanes (also called inlet and outlet guide vanes) may have theirradially-inward ends also attached to a non-rotating gas turbine statorcasing. Counterrotating "stator" vanes are also known. Conventional gasturbine blade designs typically have airfoil portions that are madeentirely of metal, such as titanium, or are made entirely of acomposite. The all-metal blades, including costly wide-chord hollowblades, are heavier in weight which results in lower fuel performanceand require sturdier blade attachments, while the lighter all-compositeblades are more susceptible to damage from bird ingestion events. Knownhybrid blades include a composite blade having an airfoil shape which iscovered by a surface cladding (with only the blade tip and the leadingand trailing edge portions of the surface cladding comprising a metal)for erosion and bird impact reasons. The fan blades typically are thelargest (and therefore the heaviest) blades in a gas turbine aircraftengine, and the front fan blades are the first to be impacted by a birdstrike.

Steam turbines include, but are not limited to, steam turbine powergeneration equipment. A steam turbine includes a steam inlet, a turbine,and a steam outlet, wherein steam turns the turbine rotor. The turbineof a steam turbine is similar to the turbine of a gas turbine. Steamturbine blades, which are generally identical to gas turbine blades,each include an airfoil portion attached to a shank portion. Rotorblades are those steam turbine blades which are attached to a rotatingsteam turbine rotor disc. Stator vanes are those steam turbine bladeswhich are attached to a non-rotating steam turbine stator casing.Typically, there are alternating circumferential rows ofradially-outwardly extending rotor blades and radially-extending statorvanes, wherein the stator vanes radially extend between, and areattached to, radially outer and inner rings. Conventional steam turbineblade designs typically have airfoil portions that are made entirely ofmetal. The all-metal blades are costly and heavy in weight which resultsin higher steam turbine prices and which requires sturdy bladeattachments.

What is needed is a lighter-weight steam turbine blade.

SUMMARY OF THE INVENTION

The steam turbine blade of the invention includes a shank portion and anairfoil portion. The airfoil portion has an operating temperature range,a design rotational speed, a blade root attached to the shank portion, ablade tip, and a radial axis extending outward toward the blade tip andinward toward the blade root. The airfoil portion also includes ametallic section and at least one elastomeric section. The metallicsection consists essentially of metal, has a first mass density, andradially extends from generally the blade root to generally the bladetip. The at-least-one elastomeric section consists essentially ofelastomer, has a second mass density, is bonded to the metallic section,and is resilient over the operating temperature range. The second massdensity is less than the first mass density. Preferably, the metallicsection and the at-least-one elastomeric section only together define agenerally airfoil shape at the design rotational speed.

Several benefits and advantages are derived from the steam turbine bladeof the invention. The metallic section radially extends generally theentire radial length of the blade to provide structural strength whilethe at-least-one elastomeric section provides lower weight. The lowerweight allows for a less-robust blade attachment. In addition, the steamturbine blade design is believed to be less costly than any possibleall-lightweight-metal hollow or solid blade design.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side-elevational view of the pressure side of apreferred construction of the steam turbine blade of the presentinvention;

FIG. 2 is a schematic cross-sectional view of the airfoil portion of thesteam turbine blade of FIG. 1, taken along lines 2--2 of FIG. 1; and

FIG. 3 is a view, as in FIG. 1, of the blade of FIG. 1, but with thepreferred erosion coating and the preferred skin removed from theairfoil portion.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, wherein like numerals represent likeelements throughout, FIGS. 1 through 3 schematically show a preferredconstruction of the steam turbine blade 10 of the present invention. Ina first embodiment of the invention, the steam turbine blade 10 includesa shank portion 12 and an airfoil portion 14. The airfoil portion 14 hasan operating temperature range, a design rotational speed, a blade root16 attached to the shank portion 12, a blade tip 18, and a radial axis20 extending outward toward the blade tip 18 and inward toward the bladeroot 16. The shank portion 12 typically includes a dovetail 22, forattachment of the blade 10 to a rotor disc (not shown), and a bladeplatform 24, for helping to radially contain the steam flow (the steamflow direction being indicated by arrows 26 in FIG. 1). A preferreddovetail (not shown) has radially-extending fingers which engage slotsin the rotor disc. The airfoil portion 14 has a leading edge 30 and atrailing edge 32, wherein the steam flow direction 26 is generally fromthe leading edge 30 to the trailing edge 32. The airfoil portion 14 alsohas a pressure (concave-shaped) side 34 and a suction (convex-shaped)side 36, wherein the steam turbine blade 10 rotates in a direction suchthat the pressure side 34 passes a reference point before the suctionside 36 passes the same reference point.

The airfoil portion 14 also includes a metallic section 28 (seen inFIGS. 2 and 3) consisting essentially of (and preferably consisting of)metal. The term "metal" includes "alloy". It is noted that a "metallicfoam", because of its foam cavities (i.e., cells), is not considered toconsist essentially of metal for the purpose of describing theinvention. Preferably, the metallic section 28 is a monolithic metallicsection. In an exemplary embodiment, the metal consists essentially of(and preferably consists of) titanium. Other choices for the metalinclude, but are not limited to, aluminum, cobalt, nickel, or steel. Themetallic section 28 has a first mass density and radially extends fromgenerally the blade root 16 to generally the blade tip 18. Even withlightweight metals, the first mass density of the metallic section 28typically is greater than generally two grams per cubic centimeter. Inan exemplary construction, the metallic section 28 has no surfacethrough-holes and no internal voids.

The airfoil portion 14 additionally includes at least one panel section38 (seen in FIGS. 2 and 3) not consisting essentially of metal, having asecond mass density, and bonded to the metallic section 28. Preferably,the at-least-one panel section 38 comprises spaced-apart first andsecond panel sections 38' and 38", and the metallic section 28 alsoincludes a rib 40 disposed between, and bonded to, the first and secondpanel sections 38' and 38". The second mass density is less than thefirst mass density. Preferably, the second mass density is less thangenerally 2.0 gram per cubic centimeter. The metallic section 28 and theat-least-one panel section 38 (which in the preferred construction shownin FIGS. 2 and 3 consists of the first, second, and third panel sections38', 38", and 38'") only together (and not separately) define agenerally airfoil shape. The number, shape, and location of theat-least-one panel section 38 is chosen by the artisan. It is noted thatthe metallic section 28 of the airfoil portion 14 may include additionalribs (such as additional rib 42) for improved stiffness and to act ascrack/delamination stoppers, and that the number and orientation of theribs is left to the artisan. For example, in addition to ribs 40 and 42which run generally radially, other ribs (not shown) may run generallychordwise or run generally along some arbitrary angle with respect tothe radial axis 20.

The choice of material for the at-least-one panel section 38 isunlimited provided such material does not consist essentially of metal,has a lower mass density than that of the metallic section 28, issuitable for use in a particular blade in a particular steam turbineenvironment, and will not debond from the metallic section 28 of theparticular blade during normal operation of the particular steamturbine. Choices for the material for the at-least-one panel section 38include, without limitation, materials consisting essentially of rigidcomposites, reinforced and unreinforced plastics, rigid foams, andmixtures thereof.

The term "composite" is defined to be any material having any (metal ornon-metal) fiber filament embedded in any (metal or non-metal) matrixbinder, but the term "composite" does not include a metal fiber (i.e.,fiber filament) embedded in a metal matrix. Preferably, when theat-least-one panel section 38 is a composite panel section, suchcomposite panel section is a layup of discrete composite laminations. Inan exemplary embodiment, the composite material consists essentially of(and preferably consists of) carbon fiber filaments embedded in an epoxy(i.e., epoxy resin) matrix binder. Other choices for the compositematerial include, but are not limited to, fiber-bismaleimide,fiber-polyimide, and other fiber-epoxy thermoset or thermoplastic resinsand mixtures thereof. Fiber-filament modulus and orientation are chosento maintain overall airfoil-portion stiffness to minimize structuralbinding of the blade under centrifugal and aerodynamic load, as iswithin the level of skill of the artisan.

The term "foam" is defined to be any material (including a polymer,ceramic, silicone, metal, and mixtures thereof) having cellular (e.g.,honeycomb) structures (regardless of size, shape, uniformity, orcontent) dispersed generally throughout the material. As previouslynoted, a "metallic foam", because of its foam cells (i.e., cavities), isnot considered to consist essentially of metal for the purpose ofdescribing the invention. In an exemplary embodiment, a polymer foam hasirregularly-shaped and preferably generally identically-sized generally10⁻¹⁶ cubic-millimeter air-containing cavities. Further examples offoams include structural foams and syntactic foams. The term "structuralfoam" is defined to be a plastic having a cellular core and integralskin, and the term "syntactic foam" is defined to be a cellular polymermade by dispersing rigid, microscopic particles in a fluid polymer andthen curing it. An example of a syntactic foam is Rohacell Foam.

In a favored enablement, the composite or foam material is thermallyremovable from the metallic section 28 at a temperature below themelting point of the metal of the metallic section 28. This allows theairfoil portion 14 to be easily repaired should it become damaged due toforeign object impacts. If the airfoil portion 14 is damaged in acomposite or foam panel section, the composite or foam material would bethermally removed, the metallic section 28 repaired, and new compositeor foam material reapplied.

Preferably, the bonding of the at-least-one panel section 38 to themetallic section 28 is accomplished by self adhesion or adhesion betweenthe at-least-one panel section 38 and the metallic section 28. Otherexamples of bonding include, without limitation, adhesive bonding(adhesive film or paste) and fusion bonding. It is noted that themetallic section 28 has a first volume, the at-least-one panel section38 has a second volume, and in an exemplary embodiment, the secondvolume of the at-least-one panel section 38 is equal to at leastgenerally twenty percent of the first volume of the metallic section 28.It is further noted that rigid composites and rigid foams are compositesand foams which are rigid over the operating temperature range of theairfoil portion 14 of the steam turbine blade 10.

It is noted that the shank portion 12 preferably is a metal shankportion. However, a composite shank portion (suitably bonded orotherwise affixed to the airfoil portion 14) may be employed inparticular blade designs. It is noted that the dovetail 22 of the shankportion 12 can be partially composite (not shown) on the pressure(concave) side. Alternatively, the dovetail 22 can have a metal wedgesystem (also not shown) to positively capture adjoining foam orcomposite sections and provide a metallic dovetail wear surface.

Surprisingly, a choice for the material for the at-least-one panelsection 38 is an elastomer, although this runs counter to theestablished wisdom in the steam turbine art of requiring the airfoilportion 14 to be made of rigid materials! An elastomer is a preferredmaterial, and a second preferred embodiment of the invention isidentical to the previously-described first preferred embodiment butwith the terminology "at least one panel section 38" replaced with "atleast one elastomeric section 46", wherein the at-least-one elastomericsection 46 consists essentially of elastomer and is resilient over theoperating temperature range, and wherein preferably the metallic section28 and the at-least-one elastomeric section 46 only together define agenerally airfoil shape at the design rotational speed. Usually, theairfoil shape will also exist at zero rotational speed, but particularapplications may call for elastomers whose resiliency is such that theairfoil shape will exist only under rotational centrifugal forces, as iswithin the design capabilities of the artisan.

The term "elastomer" as defined in Webster's Third New InternationalDictionary, means "an elastic rubberlike substance (as a syntheticrubber or a plastic having some of the physical properties as naturalrubber)". In an exemplary embodiment, the elastomer consists essentiallyof, and preferably consists of, poly(phenyldimethylsiloxane). Otherchoices for the elastomer include, but are not limited to,fluorohydrocarbons, polyorganosiloxanes like poly(dimethylsiloxanes),poly(halosiloxanes) like poly(fluorosiloxanes), nitrogen and phosphoruscontaining polymers like polyphosphazenes, poly(arylsiloxanes) likepoly(diphenolsiloxanes), as well as any copolymers prepared therefrom.It is noted that the terminology "consisting essentially of anelastomer" includes, without limitation, an elastomer containingelastomer fillers such as, without limitation, calcium carbonate, carbonblack, fumed silica, and quartz. The term "resilient" as defined inWebster's Third New International Dictionary, includes "returning freelyto a previous position, shape, or condition: as . . . capable ofwithstanding shock without permanent deformation or rupture . . ." It ispreferred that the bonding of the at-least-one elastomeric section 46 tothe metallic section 28 is accomplished by self adhesion or adhesion.Other examples of bonding include, without limitation, adhesive bonding(adhesive film or paste) and fusion bonding.

Preferably, the at-least-one elastomeric section 46 has a modulus ofelasticity of between generally 250 pounds-persquare-inch (psi) andgenerally 50,000 pounds-per-square-inch (psi) (and more preferablybetween generally 250 psi and generally 20,000 psi) over the operatingtemperature range. An elastomer that is too soft (i.e., having a modulusof elasticity less than generally 250 psi) may not be able tostructurally provide an airfoil shape, and an elastomer that is too hard(i.e., having a modulus of elasticity greater than generally 50,000 psi)may not be able to be manufactured to required close tolerances. A morepreferred range for the modulus of elasticity for the at-least-oneelastomeric section 46 is between generally 500 psi and generally 15,000psi.

The metallic section 28 has a first volume, and the at-least-oneelastomeric section 46 has a second volume. Preferably, the secondvolume is equal to at least generally twenty percent of the firstvolume. In an exemplary embodiment, the at-least-one elastomeric section46 comprises spaced-apart first and second elastomeric sections 46' and46" (and preferably a spaced-apart third elastomeric section 46'"). In apreferred construction, the metallic section 28 includes first andsecond surface recesses 48' and 48" each having an open top 50' and 50"and a closed bottom 52' and 52". It is preferred that the first andsecond surface recesses 48' and 48" each face the pressure side 34 ofthe airfoil portion 14, although one or more may face the suction side36 in a particular blade application. The first elastomeric section 46'is disposed in the first surface recess 48', and the second elastomericsection 46' is disposed in the second surface recess 48". Preferably,the metallic section 28 includes a rib 40 disposed between, and bondedto, the first and second elastomeric sections 46' and 46", wherein therib 46 narrows from the closed bottoms 52' and 52" toward the open tops50' and 50" of the first and second surface recesses 48' and 48". It isnoted that a desired location for the at-least-one elastomeric section46 is toward the blade root 16 and away from the blade tip 18 and theleading and trailing edges 30 and 32. In an exemplary construction, themetallic section 28 has no surface recesses other than those containingelastomeric sections 46.

In an alternate embodiment, the airfoil portion 14 further includes askin 54 which generally covers and is bonded to the at-least-oneelastomeric section 46, wherein the skin 54 has a modulus of elasticitywhich is at least generally ten times higher than that of theat-least-one elastomeric section 46. Such skin 54 preferably is ofcomposite or metal construction. Preferably, the skin 54 is a layup ofdiscrete composite plies or of a braided construction. In an exemplaryembodiment, any skin composite consists essentially of (and preferablyconsists of) carbon, glass, or aramid filaments embedded in an epoxy(i.e., epoxy resin) matrix binder. Other choices for the compositeinclude, but are not limited to, fiber-bismaleimide, fiber-polyimide,and other fiber-epoxy thermoset or thermoplastic resins and mixturesthereof wherein the fibers are glass, aramid, or graphite and mixturesthereof. Fiber-filament modulus and orientation are chosen to maintainoverall airfoil-portion stiffness to minimize structural binding of theblade under centrifugal and aerodynamic load, as is within the level ofskill of the artisan. Preferably the bonding of any skin composite isaccomplished by use of a separate adhesive film material or resintransfer molding or injection. Other examples of bonding include,without limitation, adhesion between the composite resin itself and thesubstrate. Typically, the skin 54 is a thin layer and may (as shown inFIG. 2) or may not also cover the metallic section 28. When present, thepurpose of the skin 54 is to give a hard face to the at-least-oneelastomeric section 46 for protection against the operating environment.

Preferably, the airfoil portion 14 moreover includes an erosion coating56 (unless the skin itself provides sufficient erosion resistance) whichgenerally covers and is bonded to the skin 54. In a desiredconstruction, the erosion coating 56 includes a metallic region 56'disposed only at generally the leading edge 30. It is preferred that theerosion coating 56 also include a non-metallic region 56" disposed fromthe metallic region 56' to generally the trailing edge 32. An example ofa material for the non-metallic region 56" is, without limitation,polyurethane, and an example of a material for the metallic region 56'is, without limitation, titanium. It is noted that the blade design goalis to use the lightest materials possible in a steam turbine blade.

In a favored enablement, the elastomer is mechanically or thermallyremovable from the metallic section 28 at a temperature below themelting point of the metal material. This allows the airfoil portion 14to be easily repairable should it become damaged. If the airfoil portion14 is damaged in the elastomer areas, the elastomer would bemechanically or thermally removed, the metallic section 28 repaired, andnew elastomer reapplied.

Preferred methods for making the steam turbine blade 10 of the inventioninclude, but are not limited to, fabricating the metallic section 28,the at-least-one panel section 38 (whether it is the at-least-oneelastomeric section 46, or whether it is made of composite, foam, etc.),and the skin 54 separately or as one unit (co-cured) using autoclave,compression mold, or injection molding techniques. If autoclave ischosen, the metallic segment 28 would act as one side of the tool, thusminimizing tooling. Preferably, the skin 54 is built up by manual ormachine layering or by braiding around themetallic-section/panel-section assembly, and then is resin transfermolded. It is noted that the metallic section 28 preferably is forged,extruded, or cast, and that the surface recesses 48' and 48" preferablyare further machined by chemical milling, electrochemical machining,water-jet milling, electro-discharge machining, or high speed machining.

The foregoing description of several preferred embodiments of theinvention has been presented for purposes of illustration. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and obviously many modifications and variations are possiblein light of the above teaching. It is intended that the scope of theinvention be defined by the claims appended hereto.

We claim:
 1. A steam turbine blade comprising:a) a shank portion; and b)an airfoil portion having an operating temperature range, a designrotational speed, a blade root attached to said shank portion, a bladetip, and a radial axis extending outward toward said blade tip andinward toward said blade root, and wherein said airfoil portion alsoincludes:(1) a metallic section consisting essentially of metal andhaving a first mass density, wherein said metallic section radiallyextends from generally said blade root to generally said blade tip; and(2) at least one elastomeric section consisting essentially ofelastomer, having a second mass density, and bonded to said metallicsection, wherein said at least one elastomeric section is resilient oversaid operating temperature range, and wherein said second mass densityis less than said first mass density.
 2. The steam turbine blade ofclaim 1, wherein said metallic section and said at least one elastomericsection only together define a generally airfoil shape at said designrotational speed.
 3. The steam turbine blade of claim 2, wherein said atleast one elastomeric section has a modulus of elasticity of betweengenerally 250 pounds-per-square-inch and generally 50,000pounds-per-square-inch over said operating temperature range.
 4. Thesteam turbine blade of claim 3, wherein said metallic section has afirst volume and said at least one elastomeric section has a secondvolume, and wherein said second volume is equal to at least generallytwenty percent of said first volume.
 5. The steam turbine blade of claim3, wherein said at least one elastomeric section comprises spaced-apartfirst and second elastomeric sections.
 6. The steam turbine blade ofclaim 5, wherein said metallic section includes first and second surfacerecesses each having an open top and a closed bottom, wherein said firstelastomeric section is disposed in said first surface recess, andwherein said second elastomeric section is disposed in said secondsurface recess.
 7. The steam turbine blade of claim 6, wherein saidairfoil portion has a pressure side and a suction side, and wherein saidfirst and second surface recesses each face said pressure side.
 8. Thesteam turbine blade of claim 6, wherein said metallic section alsoincludes a rib disposed between, and bonded to, said first and secondelastomeric sections, and wherein said rib narrows from said closedbottoms toward said open tops of said first and second surface recesses.9. The steam turbine blade of claim 1, wherein said airfoil portionfurther includes a skin which generally covers and is bonded to said atleast one elastomeric section, and wherein said skin has a modulus ofelasticity which is at least generally ten times higher than that ofsaid at least one elastomeric section.
 10. The steam turbine blade ofclaim 9, wherein said airfoil portion also includes an erosion coatingwhich generally covers and is bonded to said skin.
 11. The steam bladeturbine of claim 1, wherein said elastomer consists essentially ofpoly(phenylidimethylsiloxane).